diff --git a/product/CMFCategory/CategoryTool.py b/product/CMFCategory/CategoryTool.py
index 29d2461543684e72df71fa9b6920e5ce46b3f63c..acf39e26c9e5071afdf34de0be6b8cb056bc0ed2 100644
--- a/product/CMFCategory/CategoryTool.py
+++ b/product/CMFCategory/CategoryTool.py
@@ -634,8 +634,9 @@ class CategoryTool( UniqueObject, Folder, Base ):
       elif isinstance(category_list, (list, tuple)):
         pass
       else:
-        raise TypeError, 'Category must be of string, tuple of string ' \
-                         'or list of string type.'
+        raise TypeError, ('Category must be of string, tuple of string '
+                          'or list of string type. %s %s' %
+                          (base_category_list, category_list))
 
       if isinstance(base_category_list, str):
         base_category_list = (base_category_list, )